Generally, a liquid crystal display can be fabricated by coating a liquid crystal alignment agent on a glass substrate deposited with a transparent indium tin oxide (ITO) conductive layer, heating it to form a liquid crystal alignment film, then combining two substrates oppositely facing each other, and implanting liquid crystals therebetween. Alternatively, a liquid crystal display can be fabricated by dripping liquid crystals on one substrate and combining the substrate with another substrate oppositely facing the one substrate. The latter method is typically used in the production of 5th generation, or later, LCDs for medium- and large-sized product lines.
A polyimide resin can be used in a liquid crystal alignment film. Polyimide resin typically used for a liquid crystal alignment film can be prepared by condensing and polymerizing aromatic acid dianhydrides such as pyromellitic acid dianhydride (PMDA), biphthalic acid dianhydride (BPDA), and the like, and aromatic diamines such as para-phenylene diamine (p-PDA), meta-phenylene diamine (m-PDA), 4,4-methylene dianiline (MDA), 2,2-bisamino phenylhexafluoropropane (HFDA), meta-bisaminophenoxy diphenylsulfone (m-BAPS), para-bisaminophenoxy diphenylsulfone (p-BAPS), 4,4-bis[(aminophenoxy)phenyl]propane (BAPP), 4,4-bisaminophenoxyphenyl hexafluoropropane (HF-BAPP), and the like.
A polyimide resin for a liquid crystal alignment film that includes only aromatic acid dianhydride and diamine can provide thermal stability, chemical resistance, mechanical properties, and the like, but can also have problems such as transparency and dissolvability deterioration due to a charge transfer complex and electro-optical characteristic deterioration. Japanese Patent Laid-Open Publication No. Pyeung 11-84391 discloses a method of solving the problem by including an aliphatic cyclic acid dianhydride monomer or an aliphatic cyclic diamine in a polyimide resin for a liquid crystal alignment film. In addition, Japanese Patent Laid-Open Publication No. Pyeung 06-136122 discloses a method of introducing a functional diamine with a side chain or a functional acid dianhydride with a side chain in order to increase pretilt angle and safety of liquid crystals. In addition, U.S. Pat. No. 5,420,233 discloses development of a vertical alignment layer in a vertical alignment (VA) mode, in which liquid crystals are vertically aligned from the surface to form an LCD panel.
However, as the LCD market has recently increased, high quality LCDs are increasingly required. In addition, since LCDs are rapidly becoming larger, there is an increasing requirement for a highly productive liquid crystal alignment film. Accordingly, a liquid crystal alignment film having a low inferiority rate in the LCD manufacturing process, excellent electro-optical characteristics, high reliability, and high performance that widely satisfies different characteristics for various developing LCDs is constantly required.